An improved method of formation of filament directly from molten material

ABSTRACT

A method of making filamentary solid material by contacting the surface of a pool of molten material with a circumferential projection comprising a portion of a rotating heat-extracting member is improved if the point of entrance of the projection into the molten surface is protected by surrounding the entrance point with a nonoxidizing gas. A preferred embodiment of the present invention would additionally include a means of buffing the circumferential projection at a point subsequent to the spontaneous release of the filament formed thereon.

United States Patent 191 Mobley et al.

[451 Jan. 21, 1975 AN IMPROVED METHOD OF FORMATION OF FILAMENT DIRECTLY FROM MOLTEN MATERIAL [75] Inventors: Carroll E. Mobley, Columbus;

Robert E. Maringer, Worthington, both of Ohio [73] Assignee: Battelle Development Corporation,

Columbus, Ohio 221 Filed: Apr. 6, 1973 21 Appl. No.: 348,689

[52] US. Cl 164/66, 164/87, 264/165 [51] Int. Cl B22d 11/06 [58] Field of Search 164/66, 78, 82, 87, 276;

[56] References Cited UNITED STATES PATENTS 2,544,837 3/l95l Jordan 164/276 8/1970 King l64/87 l/1973 Mobley et al [64/87 X Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Stephen L. Peterson [57] ABSTRACT 10 Claims, 6 Drawing Figures Prior Art AN IMPROVED METHOD OF FORMATION OF FILAMENT DIRECTLY FROM MOLTEN MATERIAL BACKGROUND OF THE INVENTION The present invention relates to the field of the art where a filamentary solid is made by advancing a continuous chill surface in contact with a source of molten material.

U.S. Patent Application Ser. No. 251,985, Maringer, et al., now U.S. Pat. No. 3,838,185 dicloses a method of producing filamentary solid material directly from a pool-like source of molten material. A rotating heatextracting member having at least one circumferential projection introduces a limited and elongated area of the projection to the surface of the molten material and solidifies a filament adherent to the projection. Further rotation of the member results in the filament spontaneously releasing from the forming member while the rotating member continues its rotation back into the melt. The operation of this process creates at least three problems solved by the present invention.

First, the rotation of the heat-extracting member induces the flow of the atmosphere surrounding the member. At the outer surface of the rotating disk where the solidification of the filament takes place, the member is moving fastest (at least in excess of 3 feet per second) and this surface can drag a layer of the surrounding atmosphere into the melt surface separating the forming surface from the melt. In addition to the disturbance set up by the separation, the atmosphere is generally an oxidizing agent in relation to the melt and the flow of such an oxidizing gas into the melt at the forming surface can react with the surface and introduce oxides at the most critical location. By introducing a stream of nonoxidizing gas at the interface of the molten material and the rotating member at the point where the member enters the melt surface, the prior art process is improved since the gas introduction can be effected so as to disrupt and replace the adherent layer of oxidizing gas with the nonoxidizing gas. Any nonoxidizing gas introduced to the molten material will not form oxides at the point of initial filament solidification.

Second, the controlled introduction of a nonoxidizing gas is capable of providing a barrier to prevent particulate solid materials on the surface of the melt from collecting at the point where the rotating heatextracting member would drag such impurities into the melt at the point of initial filament solidification. The bouyant solids may be the oxide of the molten material or a flux introduced to the surface to prevent oxidation at the melt surface.

Finally, the exclusion of the oxidizing gas and particulate contaminants at the point where the rotating member enters the melt both increases the stability of the release point of the solid filament from the rotating member and promotes spontaneous filament release.

BRIEF SUMMARY OF THE INVENTION The present invention is an improvement of the process where a rotating heat-extracting member having at least one circumferential projection forms filamentary material by contacting the surface of a pool-like source of molten material so as to solidify a filamentary product on the circumferential projection that is spontaneously released. The present invention comprises the introduction of a nonoxidizing gas to the point where the rotating member enters the surface ofthe molten material. A preferred embodiment of the present invention incorporates a buffing means applied to the circumferential projection on the rotating member further improving the release of filament formed thereon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged cross-sectional view of the point where the gas is introduced.

FIG. 2 is a cross-sectional view of the preferred embodiment of the circumferential projection on the rotating heat-extracting member taken from the prior art.

FIG. 3 is an overall side view of the present invention as utilized with a single circumferential projection and a localized introduction of the nonoxidizing gas.

FIG. 4 is an overall side view of the present invention where the rotating member is partially enclosed so as to facilitate the introduction of the gas to the surface of the molten material.

FIG. 5 is an overall side view of an embodiment of the invention where the means of protecting the molten material from oxidizing gas is comprised of a solid that preferentially removes oxygen from the system as well as providing a shield for the molten material.

FIG. 6 is a top view of one embodiment of the invention where discontinuous filament is produced utilizing a buffing wheel to treat the circumferential edge of the rotating member.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a variant of the teaching of U.S. Patent Application Ser. No. 251,895, Maringer, et al., now U.S. Pat. No. 3,838,185 where a rotating heatextracting member 30 having at least one circumferential projection 31 contacting the surface 11 of a poollike source of molten material 10. Where the circumferential projection 31 has a narrow edge 32 in contact with the melt surface 11 the member 30 can be rotated at relatively high speeds so as to form a filamentary product 20. The present invention introduces to the prior art invention a source of nonoxidizing gas in a manner where the gas is directed especially to the point 51 where the edge 32 enters the melt surface 11. By the introduction of nonoxidizing gas to this point, the present invention significantly improves the prior art invention.

The prior art invention as used with the present invention is operated substantially as taught in the previously cited patent application. The molten material is in a preferred embodiment of the present invention a molten metal since such materials are normally susceptable to oxidation by the atmosphere at temperatures above their equilibrium melting points. Although the benefits accruing to a process using molten nonmetals may not be as drastically improved as that of metals the present invention is operable with any molten material having the following properties at a temperature within 25 percent of its equilibrium melting point in I(: a surface tension in the range of from 10 to 2,500 dynes/cm, a viscosity in the range from 10' to l poise and a reasonably discrete melting point (i.e., a discontinuous viscosity versus temperature curve).

The disk-like heat-extracting member in the preferred embodiment illustrated in FIG. 2 would have a radius of curvature (r) in a plane parallel the axis of rotation at the edge 32 in the range of from 0.0005 to 0.10 inch and preferably a diameter in the range of from 4 to 30 inches. The preferred rotational speed of the member 30 would yield a linear velocity at the circumference 32 in excess of 3 feet per second. The edge 32 would be in contact with the surface 11 and would not be inserted below the surface in excess of 0.060 inch. The member 30 or the portion of the member comprising the edge 32 need not be of any special material but only be capable of transmitting heat from the edge 32 into the member 30 so as to initiate solidification on the edge 32 so as to form the filament 20'. The filament 20' is the solid portion of the final filament 20 formed while the adherent edge 32 is still below the equilibrium surface 11 of the melt 10.

The crux of the present invention is the improvement of the formation and of the release of the filament 20 by preventing several detrimental effects by the introduction of a nonoxidizing gas at the region 12 of the melt surface 11. First, the gas 41 is disposed to deflect any particulate material bouyant on the surface 11 away from the entrance point 51. FIGS. 1, 3, and 4 show a layer of particulate flux 15 on the surface 11 not present in the region 12 by action of the gas 41, however, the bouyant material may also be the oxide of the molten material comprising the source material. The flow of gas need not be in a direction so as to move the flux 15 or an oxide impurity completely away from point 51 but it is sufficient to keep the bouyant material moving so a portion cannot accumulate at point 51 so as to be pulled into the melt by the motion of the edge 32.

The gas 41 need not have any specific chemical properties to perform this function, however, the process is further enhanced if oxidation of the melt surface 11 is minimized in the region 12 where the protective flux 15 is not present. This is accomplished by choosing a gas composition that is either substantially inert (as, for example, nitrogen or argon) or a gas that is a reducing agent in relation to the molten material or at least a gas that will not oxidize the molten material. Such a gas is termed a non-oxidizing gas and one skilled in the art needs no further teaching of composition since the relative oxidation properties of molten materials and gases are well known. Particular success has been experienced with molten metals utilizing the gases: acetylene, natural gas, argon, nitrogen, methane, cracked ammonia and forming gas (a mixture of approximately volume percent H and 80 volume percent N It should be understood that the gas need only be nonoxidizing at the region 12 where the edge 32 enters the melt surface 11 and therefore the gas supply may consist of a reducing gas but combustion of the reducing gas in the atmosphere will yield reducing or inert combustion products at the region 12 that will carry out the object of the present invention. Reducing gases have an advantage over relatively inert gases in that they dont simply displace the oxygen surrounding the process but they can be manipulated by combustion to actually consume oxygen yielding nonoxidizing combustion products at the critical process location. The combustion products may contain solid materials and the process as used with acetylene yields particulate carbon within the nonoxidizing gas with excellent results.

The gas 41 also operates in another manner that benefits the process. Because of the high rotational speeds of the heat-extracting member, a layer of gas comprising the surrounding atmosphere is accelerated adjacent the edge 32 by the action of viscous drag. When the process is used at high speeds, the melt may be sub jected to the injection of the surrounding oxidizing gas at the edge 32. The localized oxidation of the melt is detrimental to the process, however, an additional problem is the fact that the entrained gas separates the edge 32 from the melt 10 so as to momentarily disturb the formation of the filament 20'. By subjecting the edge 32 to a flowing stream of nonoxidizing gas the layer of oxidizing gas can be at least partially removed thereby reducing the amount of oxidation at the location of filament formation.

FIG. 3 illustrates an embodiment of the present invention where the nonoxidizing gas is impinged on the region 12 where the rotating member 30 enters the melt surface 11 through the use of a nozzle-like tubular gas conduit connected to a source 40 of the gas 41.

FIG. 4 illustrates an embodiment of the present invention where a portion of the member 30 is partially enclosed by the member 45. Nonoxidizing gas is introduced to the enclosure 45 from the gas supply 40 in a manner disposed to effect gas flow toward the region 12 and point 51. This embodiment affects the process in much the same manner as the local introduction of gas by use of a nozzle because there is some opportunity for the nonoxidizing gas to be entrained on the rotating member at the forming edge 32 by the action of viscous drag of the edge. The edge 32 has a relatively long residence time rotating in the nonoxidizing atmosphere therefore it enters the surface of the molten material substantially free of oxygen.

FIG. 5 discloses an apparatus disposed to prevent oxidizing gas from being introduced to the region 12 where the edge 32 enters the surface of the molten ma terial at point 51. The rotating heat-extracting member 30 is positioned in the same manner as the other embodiments with relation to the source of molten material 10. In this embodiment, however, a solid cover 22 is placed over the surface of the molten material so as to restrict the access of the surrounding gaseous environment to the melt surface ll. The inventive concept of this embodiment lies in selecting a material for the cover 22 that when heated will absorb or react with oxygen in the atmosphere adjacent the cover so the gas in the region between the melt surface 11 and the cover 22 will contain a nonoxidizing gas. Particular success has been experienced using a solid carbon or graphite cover and allowing heat radiated from the melt surface to raise its temperature to a point where air in contact with it is made nonoxidizing by converting the oxygen present to either carbon monoxide, carbon dioxide or a mixture of both with the remainder being essentially nonoxidizing nitrogen. A preferred embodiment of the invention would have the gas in contact with the cover 22 substantially inert with respect to the cover at its elevated operating temperature. It should be understood both in the above use of the word inert and throughout this disclosure that the gas described as substantially inert need not be one of the chemically classified inert gases such as, for example, argon, helium, and krypton. A substantially inert gas is one that will not react at an appreciable rate with any of the components of the system used. Nitrogen is substantially inert to many molten metals and therefore is described herein within the class of substantially inert gases.

Graphite has the added advantage in that it will couple with an induction heating system used to heat the melt so as its heating will not be totally reliant on radiation from the surface of the melt. In addition graphite is easily abradable and a close fitting cover can be made by using the rotating member to abrade the final fit of the opening in which the member 30 rotates. Of course a provision must be made in the cover to allow the filament 20 to exit the cover while still adherent to the edge 32.

The embodiment of FIG. 5 can be combined with the embodiment of FIG. 4 by simply adding the enclosure 45 to the rotating member and making the enclosure compatible with the cover 22. Similarly the embodiment of FIG. 5 could be combined with that of FIG. 3 by utilizing a local source of nonoxidizing gas. While the nonoxidizing gas may be locally introduced either above or below the cover 22, it is a preferred embodiment of the present invention to introduce the nonoxidizing gas to the region 16 between the cover 22 and the surface 11 of the molten material 10. 4

Both with this embodiment of the invention utilizing an oxygen getting cover and the other embodiments simply using a source of nonoxidizing gas in contact with the molten material, it should be kept in mind that there may be combinations of gases, combustion products, molten materials, and gaseous getters that are potentially hazardous. Those skilled in the art of working with oxidation-prone molten materials should be sufficiently appraised of the possible danger of mixing the aforementioned components without the need of a specific teaching regarding the behavior of all combinations of gases, temperatures, getters, and molten materials that would be safe in operation with the present invention. The following specific examples will enable one skilled in the art to understand the cooperation of the various material components of the invention without a specific recitation of all known operable material combinations.

The present invention beneficially effects the spontaneous release of the filament solely by introducing a nonoxidizing gas at the point where the heat-extracting member enters the surface of the melt, however, the release of discontinuous length filament is further improved by buffing the circumferential edge of the disk subsequent to the release of the filament. The combination of the buffing of the edge and the introduction of nonoxidizing gas greatly improves the stability of spontaneous release of the filament from the circumferential edge of the heat-extracting member. For the purposes of this invention the term buffing means a mild abrasive action induced by relative motion between the edge and another solid material. Furthermore if the buffing action is arranged so as to contact the interior surface of the notches in the rotating member disposed to produce discontinuous filament the incidence of spontaneous release is further improved. A preferred embodiment of the invention would have a buffing motion 61 directed in a direction other than parallel (askew) to the direction of motion 37 of the circumferential projection on the rotating heat-extracting member 30. A rotating wheel arrangement as depicted in FIG. 6 where the axis of rotation of the buffing wheel 60 is askew that of the rotating heat-extracting member would be one embodiment of such a system. For metals having a composition consisting essentially of iron the percentage of discontinuous filaments spontaneously releasing is further increased if the temperature of the molten metal is less than 400F in excess of the equilibrium melting point of the molten iron base.

MODE OF OPERATION OF THE INVENTION Example 1 Natural gas, flowing at about 0.5 cfm, was directed through a fli-inch-diameter nozzle, to the point of disk entrance to the surface of the molten material. The material was essentially AlSl 1330 alloy steel (0.3 wt percent C, 1.2 to 2.2 percent Mn, 0.1 to 0.7 percent Si) with the temperature of the molten steel between 2,940 and 2,980F. The heat-extracting member was a water-cooled copper disk having a single V-shaped circumferential projection in contact with the surface of the molten steel. The disk was 8 inches in diameter, /2 inch thick, and the faces of the V were disposed (6 in FIG. 2). The circumferential edge of the disk had notches disposed to generate filament of a length equal to the distance between the notches. The disk was rotated at from 250 to 270 rpm and produced steel fibers 1 inch long having an effective diameter of approximately 0.020 inch continuously for 3 hours. During operation as with all the examples the incidence of fiber sticking to the edge of the disk was significantly increased upon any interruption of the gas fiow to the area where the disk edge enters the melt surface.

Example 2 Acetylene was directed through a conventional welding nozzle (No. 3 tip) at the point where the disk enters the melt surface. The melt was comprised of molten steel of nominally SAE 1024 composition at a temperature of approximately 2,900F. The same type of disk as used in Example 1 was rotated at about 260 rpm and produced 1 inch long fiber continuously without significant fiber adherence to the disk for 20 minutes.

Example 3 Natural gas was introduced to a shroud similar to that of FIG. 4 at a flow rate of approximately 1 cfm with the shroud covering about one-third of the entire circumference of the disk. The molten material was SAE 1034 steel (with a composition of 0.35 wt percent C, 0.49 to 0.52 percent Mn, 0.28 to 0.37 percent Si) at a temperature of about 2,800F. The rotating heat-extracting member was a water-cooled copper disk 1% inches thick, and 8 inches in diameter having six V-shaped circumferential projections (four per inch) having Os of 90. Each of the six edges were notched to produce 1 inch long fiber. The disk was rotated at 210 rpm and the introduction of the gas to the shroud provides a nonoxidizing gas at the points where the six edges entered the melt surface and significantly reduced the occurrence of fiber sticking to the forming edge.

Example 4 Natural gas was introduced into the shroud used in Example 3 at a flow rate of I to 2 cfm. The molten material was nominally SAE I024 steel at 2,770F. The heat-extracting member was comprised of three abutting 8-inch diameter disks '15 inch thick, one of copper, another of aluminum, and the third of brass. Each of the disks were water cooled and had a V-shaped circumferential edge. The multiple disks were rotated at 250 rpm in contact with the melt and continuous filament issued from each disk at the same circumferential release point for each of the three forming edges. The

release point remained stable with no filament sticking while the gas was introduced to the shroud.

Example The same composite heat-extracting member and molten material as Example 4 were used with various other gases introduced to the shroud. Argon at 0.5 cfm, nitrogen at l-to 2 cfm, acetylene at 0.25 cfm, and hydrogen at 1 to 2 cfm all improved the consistency of release of the fiber formed over the process not utilizing a protective gas, however, none of the gases used in this example were as effective as the natural gas of Example 4.

Example 6 Acetylene was directed through a nozzle to the point of disk entrance to the melt as depicted in FIG. 3. In this embodiment of the invention a circular buffing wheel consisting of a heat resistant fabric was rotated in a direction opposite the disk while in contact with the disks circumferential edge. The buffing effect of the wheel increased the percentage of discontinuous filaments spontaneously releasing from the disk. The molten material was nominally SAE 1024 steel at 2,850F.

Example 7 The arrangement of Example 6 was repeated except that the circular buffing wheel had its axis of rotation askew that of the rotating heat-extracting member thereby buffing the circumferential projection at an angle. The incidence of filament sticking to the rotating member was further reduced in this embodiment over that of Example 6. This is believed to be the result of the fabric of the buffing wheel having a greater effect on the surface of the circumferential projection within the notches disposed to attenuate the filament into discrete lengths.

The invention was used to produce both discontinuous and continuous metallic filaments having an effective diameter of less than 0.060 inch. The effective diameter is the diameter of a circular filament having the same cross-sectional area as the noncircular filaments produced with the present invention. The invention is not strictly applicable either to metals or such small filament and the limitations of the invention are set out solely by the appended claims.

We claim:

1. In a method of making solid filamentary material from a pool-like source of molten material by contacting the surface of said molten material with at least one circumferential projection comprising the edge of a rotating, heat-extracting member the improvement of:

maintaining a non-oxidizing atmosphere adjacent the point where said edge enters the surface of said molten material by covering said molten material with a solid cover consisting at least partially of solid carbon disposed to remove oxygen from the atmosphere adjacent said cover.

2. The method of claim 1 where said cover is heated in order to get said cover to absorb oxygen.

3. The method of claim 1 where said cover consists essentially of graphite.

4. The method of claim 3 where said molten material is a metal.

5. The method of claim 4 where said metal consists essentially of iron.

6. The method of claim 1 including the step of partially enclosing said rotating member and introducing a gas to said enclosure.

7. The method of claim 6 where said cover consists essentially of graphite, said molten material is a metal and the gas introduced to said enclosure is substantially inert both to said metal in its molten state and said graphite cover at the elevated operating temperature of said graphite cover.

8. The method of claim 7 where said graphite cover is heated by the combination of radiant energy from the adjacent molten material and the coupling with the induction heating system used to heat said molten material.

9. The method of claim 1 including the step of locally impinging a nonoxidizing gas on the point where said edges enters said molten material.

10. The method of claim 9 where said non-oxidizing gas is introduced to the region between said cover and the surface of said molten material. 

1. In a method of making solid filamentary material from a poollike source of molten material by contacting the surface of said molten material with at least one circumferential projection comprising the edge of a rotating, heat-extracting member the improvement of: maintaining a non-oxidizing atmosphere adjacent the point where said edge enters the surface of said molten material by covering said molten material with a solid cover consisting at least partially of solid carbon disposed to remove oxygen from the atmosphere adjacent said cover.
 2. The method of claim 1 where said cover is heated in order to get said cover to absorb oxygen.
 3. The method of claim 1 where said cover consists essentially of graphite.
 4. The method of claim 3 where said molten material is a metal.
 5. The method of claim 4 where said metal consists essentially of iron.
 6. The method of claim 1 including the step of partially enclosing said rotating member and introducing a gas to said enclosure.
 7. The method of claim 6 where said cover consists essentially of graphite, said molten material is a metal and the gas introduced to said enclosure is substantially inert both to said metal in its molten state and said graphite cover at the elevated operating temperature of said graphite cover.
 8. The method of claim 7 where said graphite cover is heated by the combination of radiant energy from the adjacent molten material and the coupling with the induction heating system used to heat said molten material.
 9. The method of claim 1 including the step of locally impinging a nonoxidizing gas on the point where said edges enters said molten material.
 10. The method of claim 9 where said non-oxidizing gas is introduced to the region between said cover and the surface of said molten material. 